For a common DRAM (Dynamic Random Access Memory), to substitute for a defective memory cell and to improve production yield, a redundant circuit is arranged, for rows and columns that provides a spare word line and a spare column selection line that corresponds to and can be used to replace those of the defective memory cell.
When a wafer is tested and a defective word line is found, address data for the defective word line is prepared. Following this, a fuse is blown by a laser in accordance with the address data, and programming is performed for a defective address. As a result, when that programmed address is accessed, for example, the spare word line, which is used to replace the word line wherein the defective memory cell is present, is driven. Therefore, for the redundant circuit, an address comparison circuit is included that compares, for each access, an external row address, for example, provided for a defective row address that has been programmed. Also during a refresh process, the address comparison circuit compares a row address for a word line to be refreshed with a defective row address.
A redundant circuit for a DRAM is large and consumes a large amount of a current. In order to maintain the effectiveness and the flexibility with which a substitution can be provided for a defective cell, spare word lines and spare column selection lines are provided for each ½ or ¼ block division of a large array block, instead of for a number of smaller array blocks, and spare memory cells are available to replace all defective memory cells in the large array block.
When a thus arranged DRAM is externally accessed, or refreshed at each access, an address is compared with all addresses that have been programmed. Therefore, the current required for the address comparison circuit comprises a considerably large portion of all the current consumed. And thus, though there exist demands for reductions both in an operating current for a DRAM and in a standby current used for refreshing a DRAM, especially requested is a reduction in the current consumed by the redundant circuit.